Low power heater



Nov. 3, 1964 R. J. NEY

LOW POWER HEATER Filed Deo. 15, 1961 FlG.l.

.Emmi-mama@- INVENTOR: ROBERT J. NEY

Hl TTOR'NEY.

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United States Patent O 3,155,865 LTW PWER HEATER i.. Ney, Syracuse, NX., assigner to General Electric Company, a corporation of New York .Filed Dec. l5, wel, Ser. No. 159,718 9 Claims. (Cl. S13-346) The present invention relates to cathode ray tubes and more particularly to an improved low power heatercathode assembly for such tubes.

The desirability of a low input-power heater cathode assembly for use in cathode ray tubes such as television picture tubes and camena ltubes has been recognized. With respect to television picture tubes low heater power is particularly desirable with transistorized battery-powered television receiver circuitry where battery power drain must be minimized. In the camera tube field, infrared and low light level red sensitive devices may be limited in performance, particularly in signal to noise ratio, by the extraneous heat radiated from the electron beam generating portion of the tube. Moreover in camera tubes required to operate with an electron beam-scanned target which is refrigerated, for example to liquid nitrogen temperatures, the problem of suppression of undesired heat radiation from the electron gun is substantially decreased by reducing the input heater power requirement.

Accordingly a principal object of the present invention is to provide an improved heater-cathode assembly for cathode ray tubes and the like having minimal heater input power requirements.

Another object is to provide a heater-cathode assembly of the character described which is mechanically rugged, relatively low cost, and easy to manufacture and assemble.

Another object is to provide a heater cathode assembly of the character described in which the heat developed by the heater is efficiently transferred to the thermally ernissive cathode with a minimum of extnaneous heat loss from the heater leads or otherwise.

These and other objects of the present invention will be apparent from the following description and the accompanying drawing wherein:

FlGURE l is a sectional view of a portion of an electron gun including a cathode-heater assembly constructed in accordance with the present invention;

FlGURE 2 is a cut-away perspective view of a portion of the structure of FIGURE l;

FGURE 3 is a partially broken-away fragmentary view of a portion of the structure of FIGURE 1, taken on the line 3-3 thereof;

FIGURE 4 is la view of another form of a portion of the structure of FIGURE l; and

FIGURE 5 shows another form of a portion of the structure of FlGURE l.

Referring to the drawing, the low heater power cathodeheater assembly of my invention includes an inverted cup-shaped cathode 2 on the exterior surface of the transverse top wall d of which is provided a suitable thermally electron emissive coating 6, such as a layer of barium oxide. The diameter of the top wall 4 is substantially no larg'er than that of the emissive coating 6 so as to minimize heat loss by radiation from the top wall. Depending from the top wall 4 is a cylindrical skirt S forming the side wall of the cathode cup and shown as having a length about equal to one-third the top wall diameter. The cathode is supported by a plurality of depending legs 10, shown for example as three in number, and which may consist of small cross-section metallic electrically conductive material of low heat conductivity, such as nichrome. The three legs are pyramidally arranged with approximately isosceles tetra hedral angles to `afford optimum strength and thereby per- 3,155,865 Patented Nov. 3, 1964 ICC mit the legs to be of minimum cross section. Preferably the legs l0 should have as long a length in proportion to the cross sectional area lof each as possible, so as to reduce the conduction heat loss from the cathode. Desirably the length-to-area ratio ofthe legs 10 may be over 30,000 units per square unit, and in practice it has been found that the conduction heat loss through the legs is thereby reduced to less than 2% of the ytotal heat input to the cathode.

Situated entirely within 'the inverted cup-shaped cathode is the heater 15. The heater and heater leads or end portions 18 are formed of a common integnal continuous elongate electrical conductor which may be, for example, a single filament of tungsten wire. In order to minimize heat loss from the heater leads or end portions 18 relative to desired heat transfer to the cathode the iilamentary heater is arranged with its middle portion wound in a coil 20 consisting of a relatively large number of turns and having such dimensions as to fit entirely within the invertedv cup-shaped cathode, with the axis of the coil generally parallel to the transverse top wall 4. The heater coil is wound on an electrically insulative support 22, preferably consisting of a rectangular ceramic slab, so dimensioned as to lit within the cathode cup 2. In an actual embodiment employing an 80 mil outside diameter' cathode cup, for example, and ea heater coil support slab 22 havingdimensions of about 50 by 50 mils square and l0 to l5 mils thick, it was found possible to wind some forty turns of 1/2 mil diameter tungsten Wire on the support 22, thereby providing a total length of wire on the support 22 of some five inches, and fitting entirely within the cathode cup. The edges of the core slab 22 are preferably somewhat rounded off so as to minimize the stresses at the bends in the turns of the heater coil.

The heater 16 is supported in place wtihin the inverted cup cathode 2 by two tabs 40, 42 which may be integral with the cathode side wall S and `are folded radially inward beneath A the heater.

To prevent short-circuiting of -the turns of the heater coil 20, as well as to provide additional mechanical support of the heater wire, the supporting core or slab 22 and coil of heater wire wound thereon is preferably coated with an electrically insulative material 24 such as alumina, in an integral blanket. Alternatively the wire itself of the coil 20, or the individual turns of the coil 20, may be covered with suitable insulation such as alu mina, as shown in FIGURE 4. The core 22 serves to support the upper courses of each turn of coil 20 closely adjacent the top wall 4 of the cathode for good heaty transfer thereto, but if the coil 20 itself is of sufficient strength to be self supporting, some or all of core 22 may be eliminated. ,f

The integral end portions of the heater element forminng the leads is are brought out beneath the cathode cup 2 and extendI to heater terminals 30 mounted in an insulative support 32. The leads 18 are connected to terminals 30 by collars 34. The very large lengthof heater wire which the construction described permits to be disposed within the cathode, in proportion to the dimensions of the cathode, enables theheater leads 18 to be relatively long so as to minimize heat loss from the heater by conduction without incurring an objectionably large heat loss by heat generation in, and radiation from the heater leads themselves. The construction describedY permits the ratio of the lentgh of wire in coil 20 to thel length of one lead 1S to exceed l5 or 20 to l, with a corresponding minimizing of heat loss from the leads 18 to l0 percent or less of the total heat input to the coil 20. Thus heat losses are minimized, and effective heat transfer to the cathode is maximized by a construction according to the present invention.

The structure described has many advantages. Heat losses in the heater leads are minimized yet reliability and ease of fabrication are enhanced by the integral construction of the heater coil and heater leads. Another advantage of the coil heater is its increased electrical resistance and resulting ability to operate at higher voltages, such as 6.3 volts. The long coil also has the advantage of better inhibiting the generation of undesirably high localized temperatures when temporarily subjected to excessive currents, as for example when initially energized. In addition to providing mechanical support for the heater 16, the tabs 4), 42 also serve as heat radiation shields to block radiation heat loss beneath the cathde 2, and thereby further conserve heater power. Further mechanical support for the heater i6, and enhanced rigidity of the assembly, may he provided by lling the space Within the cathode cup 2 with a thermally stable electrically insulative material S0, such as alumina, which may be applied as a slurry and allowed to dry in place. Such filling material also optimizes heat transfer to the underside of cathode surface 4.

It will be appreciated by those skilled in the art that the invention may be carried out in various ways and may take various forms and embodiments other than those illustrative embodiments heretofore described. Accordingly it is to be understood that the scope of the invention is not limited by the details of the foregoing description but will be deined in the following claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side wall, a transverse top wall surmounting said side wall for supporting an emission surface of thcrmionic electron emissive material, a continuous elongate conductive heating element arranged in a coil, means for supporting said coil Within said cathode, said coil being wound around said supporting means with the axis of said coil extending generally transversely, conductors depending from said coil forming leads for energizing said heating element, and a coating of electrically insulative material on said coil.

2. A heater for assembly with a thermionic emissive cathode of inverted cup-shape having a side wall surmounted by a transverse top wall for supporting thermionic electron emissive material comprising an electrically insulative support adapted to be carried by said cathode therewithin said insulative support having a transversely extending top surface adapted to be positioned opposite the undersurface of said top wall and having a dimension normal to said top surface less than the major dimenson of said top surface, a continuous integral elongate electrically conductive heating element including end portions separated by a middle portion, said middle portion being coiled around said support with the axis of said coil extending generally transversely, and said end portions depending from said middle portion to form integral leads for energizing said heating element.

3. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side Wall, a transverse top wall surmounting said side wall for supporting an emission surface of thermionic electron emissive material, a. continuous elongate conductive heating element including end portions separated by a middle portion, said middle portion being arranged in a coil, means for supporting said coil within said cathode, said coil being wound around said supporting means with the axis of said coil extending generally transversely, said end portions depending from said coil forming leads for energizing said heating element, and a coating of electrically insulative material on said coil.

4. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side Wall, a transverse top Wall surmounting said side wall for supporting thermouic electron emissive mal terial, an electrically insulative support carried by said cathode and extending transversely therewithin, and a continuous elongate electrically conductive heating clement coiled around said support with the axis of said coil extending generally transversely.

5. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode liaving a side Wall, a transverse top wall surmounting said side wall for supporting thermionic electron emissive material, an electrically insulative support carried by said cathode and extending transversely therewithin, a continuous elongate electrically conductive heating element including end portions separated by a middle portion, said middle portion being coiled around said support with the axis of said coil extending generally transversely, and said end portions depending from said middle portion to form integral leads for energizing said heating element, ratio of the length of said heating element coiled in said middle portion to the length of one of said leads being at least l0 to 1.

6. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side wall, a transverse top wall surmounting said side wall and adapted to support a layer of thermionic electron emissive material, an electrically insulative support carried by said cathode and extending transversely therewithin, a continuous integral elongate electrically conductive heating element including end portions separated by a middle portion, said middle portion being coiled around said support with the axis or said coil extending generally transversely, said end portions depending from said middle portion to form integral leads for energizing said heating element, and a coating of electrically insulative material on said coil.

7. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a. side wall, a top wall surmounting said side wall and including a layer of thermionic electron emissive material, an electrically insulative support carried by said cathode and extending transversely therewithin, a continuous integral elongate electrically conductive heating element of nichrome including end portions separated by a middle portion, said middle portion being coiled around said support with the axis of said coil extending generally transversely, and said end portions depending from said middle portion to form integral leads for energizing said heating element, a coating of* electrically insulative material on said coil.

8. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side wall, a transverse top wall surmounting said side wall and adapted to support a layer of thermionic electron ernissive material, an electrically insulative support carried by said cathode and extending transversely therewithin, a continuous integral elongate electrically conductive heating element including end portions separated by a middle portion, said middle portion being coiled around said support with the axis of said coil extending generally transversely, and said end portions depending from said middle portion to form integral leads for energizing said heating element, the ratio of the length of said heating element coiled in said middle portion to the length of one of said leads being at least l() to l, a coating of electrically insulative material on said coil, and a plurality of pyramidally-arranged legs connected to said cathode for supporting the same.

9. A heater-cathode assembly for an electron gun or the like comprising an inverted cup-shaped cathode having a side wall, a top wall surmounting said side wall and including a layer of thermionic electron emissive material, an electrically insulative support carried by said cathode and extending transversely thercwithin, a continuous integral elongate electrically conductive heating element including end portions separated by a middle portion, said middle portion being coiled around said Wwf' References Cited in the iile of this patent UNITED STATES PATENTS Engel Apr. 17, 1934 Segerstrom Jan. 1, 1946 Gall Feb. 20, 1951 Senior et al. June 14, 1960 

4. A HEATER-CATHODE ASSEMBLY FOR AN ELECTRON GUN OR THE LIKE COMPRISING AN INVERTED CUP-SHAPED CATHODE HAVING A SIDE WALL, A TRANSVERSE TOP WALL SURMOUNTING SAID SIDE WALL FOR SUPPORTING THERMIONIC ELECTRON EMISSIVE MATERIAL, AN ELECTRICALLY INSULATIVE SUPPORT CARRIED BY SAID CATHODE AND EXTENDING TRANSVERSELY THEREWITHIN, AND A CONTINUOUS ELONGATE ELECTRICALLY CONDUCTIVE HEATING ELEMENT COILED AROUND SAID SUPPORT WITH THE AXIS OF SAID COIL EXTENDING GENERALLY TRANSVERSELY. 